Carburetor



9 s. F. HUNT 2,450,831

' cmaunn'ron Filed Aug. -11, 1943 mvuma.

AGENT FIG. I

Patented 5, 1948 mm STATES.

l 'zgisasai f cmmme'roa Scott E. Hunt, Mei-iden, assignments, to NilesConn., 'assignor, by mesn'e -Bement-Pond Company,

West Hartford, Conn., a corporation of New Jersey I Application august11, 1943, Serial No. 498,151

- 1 The present invention relates to carburetors, and especially tomixture control systems for carburetors associated with internalcombustion engines used on aircraft.

An internal combustion engine of the type used on aircraft operates mosteconomically on a lean fuel and air mixture. However, such a leanmixture will not produce the maximum power output of which the engine iscapable. Furthermor, the use of a lean mixture under certain conditions,as when operating at high altitudes, for example, will cause the engineto overheat. It is, therefore, customary to" provide, in connection withcarburetors used on engines of this type, a manual control. arrangementbywhich.

, the fuel and air mixture supplied to the engine may be selectively setat either a. rich or a lean value; depending upon the various flightconditions encountered. As a further control of the fuel and air mixturesupplied to the engine,

there is sometimes provided a valve which opens 1 automatically underhigh load conditions to enrich'the mixture, regardless of the positionof the manual control. This additional valve is usually set to open at acertain value of load' on the engine, as measured by the quantity of airor by the quantity of fuel flowing to the engine. For optimum economyand performance, it would be desirable to open this valve at a highervalue of engine load when the mixture control is in its lean positionand at a lower value of engine load when'the, mixture control is in itrich position. In previous carburetors, however, this enrichening valvehas been set to open at a predetermined value of engine load, regardlessof the setting of the manual mixture control. The load value at whichthis valve opens is a compromise between the load value which would bebest when the mixture control isin lean position and the loadvalue'which.

A further object 'of the present invention is.

to provide, in a carburetor equipped witlra con- -trol member movable toa first position in which the carburetor supplies a lean mixture to theI 55 cation of Milton E. Chandler, Serial No. 490,281,

' engine and to a second position in which the '7 Claims. (Cl.- 261- 41)carburetor supplies a rich mixture to the engine,

improved means for enriching themixture sup-. plied to the engine inresponse to the variations .in the engine load, which means operate at5v different load values depending upon the position of the mixturecontrol member.

Other objects and advantages of the present Y invention will becomeapparent from a consideration of the appended specification, claims anddrawing, inwhich I Figure l is a somewhat diagrammatic illu'stration ofan aircraft carburetor embodying my invention, and r Figure 21s agraphical illustration of the rela-.

tionship between the fuel and air ratio and the air flow thru thecarburetor of Figure ,1.

In the drawingjthere is shown, a carburetor body portion ill thru whichair flows from an inlet ll thru a passage l2 to an outlet [3. In

flowing thru the passage l2, the air passes a Venturi restriction M, athrottle l5, and a fuel discharge nozzle l6. k

A second air passage connects the inlet l l and the throat of" theVenturi restriction I4. 'This 5 second air 'passage may be traced fromthe inlet ll thru a plurality of impact tubes I'I, whose open endsproject into the inlet il, a vent ring passage l8 interconnecting theimpact tubes IT, a conduit 20, an expansible chamber 2| in a 0 pressuremeter 22, a restriction 23, an expansible chamber 24 in the pressuremeter 22, a con-' duit 28, a chamber 30, and a conduit 3| to the throatof Venturirestriction l4. i A bellows 32 is mounted in the chamber 30,

35 and operates a valve 33 which controls the flow of air from thepas'sage 28 into the chamber 30. The bellows 32 is preferably filledwith nitrogen or other inert temperature responsive fluid, so that theposition of valve 33 is 40 determined by the temperature and pressure ofthe air in the chamber 30, and hence'by the density of that air.

- The valve 33 restricts the flow of air thru the second passage justdescribed in such a manner that the pressure differential betweenchambers 2| and 24 is an accurate measure of the rate pf mass air flowthru the passage l2. Errors;,due

to changes in the density of the air with a1titude and temperature andalso those errors due to the inherent limitations of a meteringrestriction of the Venturi t pe, are substantially eliminated by theoperation of valve 33. This type of metering error compensation ismore'completely described and claimed in the co-pending appli- P TENT?FFIcB 3 filed June 10, 1943, now Patent No. 2,393,144, issuedJan.15,1946.

The fuel passing thru the carburetor comes from a fuel pump orothersource Of fuel under pressure (not shown). From this source, .the fuelpasses thru aconduit 34. a fuel regulator unit 25, a conduit 35, amixture control valve 36, a jet system 31, a conduit 38, -a pressureregulator valve 48, and a conduit 4| 'to the discharge nozzle |6.--

The pressure meter 22 include a casing 42 which is separated by threeflexible diaphragms 43, 44 and 45 into four expansible chambers 46, 24,2| and 41. A sleeve 48 is attached to the central portions of thediaphragm-s 43, 44 and 45. An annular flange 58 on the interior of oneend of the sleeve acts as a valve, and cooperates with a tapered seatformed on a post 52 extending thru the center of the sleeve 48.

The internal diameter of the sleeve 48 is greater than the externaldiameter of the post 52, so that the position of the valve 58 relativeto the seat 5| controls the flow of fluid thru the sleeve 48 between thechambers 46 and 41. v

The fuel regulator unit 25 includes a housing 53 separated by a flexiblediaphragm 54 into a pair of expansibie chambers 55 and 56. The diaphragm54 supports at its central portion a valve 51. The valve 51 controls theflow of fluid between the conduit 34 and the chamber 56,

which is directly connected with conduit 35. The valve 51 is balancedagainst variations in inlet pressure. The position of valve 51 isdetermined by the difference between the pressures in the chambers 55and 56, and by the' compression of a spring 58, which urges the valve 51in an opening direction. The chambers 55 and 58 are connected byarestricted passage 68.

The mixture control valve 36 includes a disc valve member 6| fixed on ashaft 62 which may be rotated by means not shown, as, for example, amanual lever. The disc valve member 6| is designedto control the flow offuel from conduit 35 thru a chamber 63 to conduits 64 and 65. When thedisc valve 6| is'in the position shown in the drawing, the fuel is freeto enter both conduits 54 and 65. As the shaft 62 is rotated, the discvalve 6| may be moved to another position wherein it permits the flow offuel from chamber 63 only thru conduit 65. If desired, the disc -valve6|. may also be designed so that in certain angular positions, itcompletely cuts off the flow of fuel from the conduit 35.

The jet system 31 includes a pair of jets or restrictions 66 and 61which receive fuel thru the conduit 65, and a jet 68 which receives fuelthru the conduit 64. Fuel flowing thru the jets 61 and 68 also passesthru a jet 10 before flowing out of the jet system 31 into the conduit38. A poppet valve 1| is positioned in the jet 61 so as to be urgedtoward open position by-the pressure differential which causes the fuelflow thru the jet. A spring 12 biases the poppet valve 1| .to closedposition. A poppet valve 13 is positioned in the jet 88 so as to beurged in an opening direction by the pressure differential which causesthe fuel flow thru that jet.

is apertured as at 15, so that even when the valve 13 is seated, a smallamount of fuel may pass thru the jet 68 and the apertures 15. It will bereadily apparent that a fixed restriction in parallel with the jet 58may be used instead of the apertures 15 in the valve 13, if desired.

The pressure regulator includes a casing 16 A coil spring 14 biases thevalve 13 to closed position. The poppet valve 13 4 separated by adiaphragm 11 into a pair of expansible chambers 18 and 88. The diaphragm11 carries a valve 8| at its center. The valve-8| controls the flow offuel from chamber 88, which is connected to conduit 88, to the outletconduit 4|. The valve 8| is balanced against changes in outlet pressure,so that the position of valve 8|. is determined by the difference inpressures bc-, tween the chambers 18 and 88, and by the tension of thespring 82 whichbiases the valve 8| toward closed position. The chamber18 is connected thru a conduit 82 to the vent ring l8. The pressure inchamber 18 is small as compared to the sum of that pressure and thestrength of spring .82. Therefore the pressure 'in chamber 18' has onlya small controlling effect on the position of valve 8|. The connectionof chamber 18 thru conduit 82 to vent ring |8 serves as a vent for thechamber 18 so as to permit ready movement of the diaphragm 11 inresponse to variations in pressure in the chamber 88, and also to varythe pressure in chamber 18 according to changes in barometric pressure.

Operation A portion of fuel entering the fuel regulator 25 passes thruchamber 56, restriction 88, chamber 55, a conduit 83, chamber 48 ofpressure meter 22, thru the center of sleeve 48, chamber 41, and aconduit 84 to chamber 88 of the pressure regulator 48. i

The quantity of fuel entering the'carburetor is measured by the jetsystem 31, and is controlled by varying the pressuredliferential acrossthat system. The pressure downstream from the jet -system 31 ismaintained substantially constant by the pressure regulator 48, whilethe pressure upstream from the jet system 31 is controlled by the fuelregulator 25. The fuel regulator 25 is in 0 turn controlled by thepressure meter 22.

The difference in pressure between chambers 2| and 24 of the pressuremeter 22 is a measure of the quantity of air entering the carburetor, aspreviously described. This differential pressure acts on the sleeve 48in adirection tending to move the valve 58 against the seat 5|. Thispressure differential is opposed by the pressure in chamber 46, and isaided by the pressure in chamber 41. The pressure in chamber 41 is thesame as that in chamber 88 of pressure regulator 48, and hence is thesame as the pressure on the downstream side of the jet system 31. Thepres,- sure in chamber 46, on the other hand, is the same as that inchamber'55 of 'fuel regulator 25. Since the latter chamber is connectedto the upstream side of the jet system 31 thru the fixed restriction 68,it may be seen that the pressure in chamber 55 is a measure of thepressure on the upstream side of the jet system 31. Therefore, thepressure meter 22 controls the pressure in chamber 55 in accordance withthe unbalance between a differential pressure indicative of the quantityof air entering the carburetor and a second differential pressureindicative of th quantity of fuel entering the carburetor. When thesetwo differential pressures become unbalanced, the pressure meter 22operates to vary the pressure in chamber 55 in a direction to restorethe balanced condition, and at the same time varies the flow thru thefuel regulator unit 25 so as to maintain the pressure differentialacross the let systom 31 proportional to the quantity of air enteringthe carburetor.

When the mixture control valve 6| is in the position shown in thedrawing both the conduits .it and 65 may receive fuel from the chamber88.

This is the rich. position of valve 8|. When'the valve 61 is in thisposition. fuel may flow thru all three of the jets 8!, 6,1 and 68. Therelationship between the air ilowand the fuel and air ratio 5; underthese conditions is illustrated by the characteristic C in Fig. 2. Atlow values of air flow,

the pressure differential across thejet system 3 as controlled by fuelregulator 25, is also low. The

springs 12 and 14 are strong enough to maintain in.

their associated poppetvalvesflll and I; closed under these conditions;4 'Iliereforethe fuel flow is determined by the cross-sectional area ofjet 66 and the apertures 15 thru the poppet valve 13.

If it is now assumed that the throttle is opened 15 wider so that theair fiow increases, the pressure differential across the jets will belikewise in- I creased by the action of the fueliegulator- 25. When theair fiow exceeds a predetermined value,

' which ma be that value indicated by the ordinate 20 A in Figure'2, thepressure differential across jet 68 becomes sufilcient to overcome thespring H.

The poppet valve 13 then opens, increasing the ratio of fuel to'air' inthe mixture supplied to the engine. If the air fiow continues toincrease until it reaches a value such as that indicated by the ordinateB in Figure 2, the pressure differential across jet 61 becomessufilcient to'overcome spring 12 which is stronger than spring 14,

thereby opening the poppet valve .H and further increasing the fuel toair ratio.

When the mixture control valve 6! is in its lean position-the conduitBills closed, and the conduit 65 remains open. Under those conditions,no fuel fiows thru jet 68. v The relationship between the fuel and airratio and the air flow then obtained is illustrated by thecharacteristic D in Figure 2. There it may be seen that as the air fiowincreases the fuel to air ratio remains substantially constant until anair fiow indicated by the ordinate B is reached. Then the pressuredifferential across jet Bl opens the poppet valve ll, acting againstspring I2, and increasing the fuel to air ratio.

It may therefore be seen that I haveprovided a mixture control systemwherein'th fuel to air ratio is maintained at a low economical valueuntil a very high air. flow is encountered when a manually operablemixture control is in a lean position, but that the fuel to air ratio isincreased at a lower .value of air flow when the manually operablemixture control is in its rich position.

While I have shown and described a preferred 4 embodiment of myinvention, other modifications thereof will occur to those skilled. inthe art, and

I therefore intend that my invention shall be limited only by theappended claims.

I claim as my invention: l 1. A fuel supply system for an internalcombustion engine, comprising a first main conduit for conveyingcombustion air t-o'said engine, a second main conduit for conveying fuelto said engine,

first and second parallel branch conduits connected in series with saidsecond main conduit, a

mixture control valve located at a junction of said parallel branchconduits and said second main conduit, said mixture control valve beingmovable between a first position wherein only said first parallel branchconduit is opened to the flow of fuel and a second position wherein both7 of said parallel branch conduits are openedto the flow of fuel, firstand second fixed metering restrictions in said first and second parallelbranch conduits, respectively, means responsive to the rate of fiow ofair thru said first main conduit for I. 7 anneal.

regulating" the fuel pressure diflerential across said restrictions tocontrol the rate of fiow' offuel therethru, said pressure differentialregulating means, said restrictions and said mixiture control valvecooperating w en said mixture control valve is in said first p ition tomaintain a first predetermined fuel-to-air ratio and when said mixturecontrol'valve is in said second position to maintain a-secondpredetermined fuel-to-' air. ratio'greater than said first ratio, firstand second enrichment valves connected in parallel with said first andsecond restrictionsrespectiVely. each said enrichment valvebeingwtedupon in an opening sense by said fuel pressu differential, andfirst and second springs assoc ated with said first, and seconden'richmentvalves, 'respec;= tively, to bias said valves toward closedposition,

said first spring being stronger than said second spring, said valvesand springs cooperating with, said pressure differential regulatingmeans to in-' crease the fuel-t-o-alr ratio above said, fi rstpredetermined value at a first fuel pressure differen- 'f tlal valuewhen said mixture control valve isii-in' said first position and toincrease the fuel-to-air ratio above said second predetermined value ata second lower fuel pressure differential value when said mixturecontrol valve is in said second position. v

2. A fuel supply system for an internal combustion engine, comprising afirst main co nduit for conveying combustion air to said engine .asecond main conduit for conveying fuel to sd d engine. first and secondparallel branch conduits connected in series with said second mainconduit,-a

mixture control valve located at a junction of'said parallelbranchconduits and said second main conduit, said mixture control valvebeing movable between a firstposit-ion wherein only said first parallelbranch conduit'is opened to the flow of fuel and a second positionwherein both of said parallel branch conduits are opened to the fiow offuel, first and second fixed metering restrictions in said first andsecond parallel branch conduits, respectively, means responsive to therate of flow of air thru said first main conduit for reg-v ulating thefuel pressure differential across said restrictions to control the rateof fiow of fuel therethru, said pressure differential regulating means,said restrictions and said mixture control valve cooperating-when saidmixture control valve is in said firs-t position to maintain a firstpredetermined fuel-to-a'ir ratio and when said mixture control valve isin said second position to maintain a second predetermined fuel-to-airratio greater than said first ratio, enrichment valve means connected inparallel with said restrictions, said enrichment valve means being acted.upon in an opening sense by said fuel pressure differential, and springmeans for biasing said enrichment valve means toward closed position,and means to vary a force acting on said enrichment valve means in avalve-opening sense upon movement of said mixture control valve fromsaid first to said second positions, said enrichment valve means andsaid force varying means cooperatin with said pressure differentialregulating means to increase the fuel-to-air ratio above said firstpredetermined value at afirst fuel pressure differential value when saidmixture control valve is in said first position and to increase thefuelto-air ratio above said second predetermined value at asecond lowerfuel pressure differential value when said mixture control valve isinsaid second position. 5 a 3. A fuel supply system for an internalcombustion .engine, comprising a first main conduit for c yingcombustion air to said engine, second main conduit for conveying fuel tosaid engine, first and second parallel branch conduits connected inseries with said second main conduit, a mixture control valve located ata junction of said parallel branch conduits and said second mainconduit, said mixture control valve being movable between a firstposition wherein only said first parallel branch conduit is opened toth: flow of fuel and a second position wherein both of said parallelbranch conduits are opened to the fiow of fuel, first and second fixedmetering restrictions said first position to maintain a first predeter-'mined fuel-to-air ratio and when said mixture control valve is in saidsecond position to maintafn a second predetermined fuel-to-air ratiogreater than said first ratio, an enrichment valve connected in parallelwith one of said restrictions, said enrichment valve being acted upon inan opening sense by the pressure drop across said econd restriction, anda spring for biasing said enrichment valve toward closed position, saidonrichment valve cooperating with said pressure differential regulatingmeans only when said mixture control valve is in "said second positionto in-- crease the fuel-to-air ratio above said second predeterminedvalue at a predetermined fuel pressure differential value.

4. A fuel supply system for an internal combustion engine, comprising afirst main conduit for conveying combustion air to said engine, a secondmain conduit for conveying fuel to said engine, first and secondparallel branch conduits connected in series with said second mainconduit, a mixture control valve located at a junction of said parallelbranch conduits and said second main conduit, said mixture control valvebeing movable between a first position wherein only said first parallelbranch conduit is opened to the ilow'of fuel and a second positionwherein both of said parallel branch conduits are opened to the flow offuel, first and second fixed metering restrictions in said first andsecond parallel branch conduits, respectively, means responsive to therate of flow of air thru said first main con-' duit for regulating thefuel pressure diiferential across said restrictions to control the rateof flow of fuel theretliru, said pressure differential regulating means,said restrictions and said mixture control valve cooperating when saidmixture control valve is in said first position to maintain a firstpredetermined fuel-to-air ratio and when said mixture control valve isin said second position to maintain a second predetermined fuel-toairratio greater than said first ratio, enrichment valve means connected inparallel with said restrictions, said enrichment valve means beingmovable in response to the pressure in said second branch conduitbetweensaid mixture control valve and said second restriction, spring means forbiasing said enrichment valve means, toward closed position, saidmixture control valve means being effective upon movement to said secondposition to vary said pressure in an enrichment valve opening sense,said enrichment valve means cooperating with said pressure difierentialregulating mean to increase the fuel-to-air ratio above said firstpredetermined value at a first fuel pressure differential value whensaid mixture control valve is in said first position and to increase thefuel-'to-air ratio above said second predetermined value at a secondlower fuel pressure differential value when said mixture control valveis in said second position.

5. A charge forming device for an internal combustion engine, comprisinga conduit for combustion air flowing toward said engine, means forcontrolling the flow of air thru said conduit, a conduit for fluid fuelflowing toward said engine, means for controlling the flow of fuel thrusaid fuel conduit, means for coordinating the operation of said fuelfiow control means and said air fiow control means to maintain apredetermined fuel-to-air ratio, first means associated with saidcoordinating means for varying said ratio, an operator for said firstmeans movable between a first position wherein said coordinating meansand said ratio varying means cooperate to maintain a first predeterminedratio and a second position wherein said coordinating means and saidratio varying means cooperate to maintain a second greater ratio, andsecond means including a plurality of successively opening fuel valvesin said first means for varying said ratio to increase :c'aid ratioabove said first value when said operator is in" said first position andthe rate of air fiow exceeds a first predetermined value, and toincrease said ratio above said second value when said operator is insaid second position and the rate of air flow exceeds a second valuelower than said first value.

6. Fluid fi-ow controlling apparatus, comprising first and secondparallel conduits leadingfrom a common inlet to a common outlet, firstand second restrictions in said first and second conduits, respectivcly,a selector valve in series with said conduits and movable between afirst position wherein flow is permitted only thru said first conduitand a second position wherein flow is permitted thru both said conduits,first and second by-pass conduits connected in parallel with said firstand second restrictions, respectively, first and second pressureresponsive valves in the respective bypass ccnduits, said pressureresponsive valves being movable in an opening direction in response tothe fluid pressure differential across said restrictions, first andsecond springsbiasing said first and second valves, respectively, towardclosed position, said second spring being weaker than said first springso that said second valve opens at a lower value of fluidpressure-differential than said first valve.

, 7. Fluid fiow control apparatus, comprising a main conduit, 0, pair ofparallel branch conduits connecting two spaced portions of said mainconduit, a selector valve at one of the junctions of said branchconduits with said main conduit, said selector valve being movablebetween a first position wherein only one of said branch conduits isopen and a second position wherein both of said branch conduits areopen, a metering restriction in each of said branch conduits, saidselector valve being effective upon movement to said first and secondpositions to establish respectively first and second relationshipsbetween the fluid pressure differential between said portions of saidmain conduit and the quantity of fiuid per unit of time therethru,passage means arranged for fiow parallel to said branch conduits, valvemeans in said passage means subject to said fluid pressure differential,said diiierential acting on said valve means in an opening sense,springnmeans biasing said valve means to closed position, and

means including said selector valve to vary a force acting on said valvemeans in a valve-opening sense upon movement of said selector valve fromsaid first to said second positions, so that said valve means commenceto open when said selector valve is in said first position at a firstpredetermined value or said pressure differential and when said selectorvalve isin said second position at a second lower value or said pressurediflerential.

sco'rr I.

Romances cum The following reference: are of record in the tile of thispatent:

Number Number 523395 15 cameo Automotive Industries, June 15, 1941,pages 10 mm'nn s'rarns rwmma Name Date Reeder Mar. 31, 1914 MacBrydeJune 15, 1920 Abernethy et a1 Nov. 9, 1926 Lister June 20, 1939 BoyceJune 11, 1940 Udale Dec. 2, 1941 Mock et al Feb. 16, 1943 Mock Oct. 24,1944 FOREIGN PATENTS Country Date Great Britain July 25, 1940 France May15, 1935 o'rm ammnucss

